Common twist drills are a very standardized tool and when purchased new the geometry at the cutting end of twist drills is a standardized geometry generally selected by the Metal Cutting Tool Institute as the best geometry for all general purpose drilling and is an included point of 118.degree., a lip relief angle of 6.degree. to 18.degree. (depending on drill diameter), a chisel edge angle of 120.degree.-130.degree., and the center of the chisel edge accurate to within 0.003 inch with the axis of the drill. Drills with this standarized point geometry are purchasable at hardware stores and industrial supply distributors by homeowners, hobbyist, auto mechanics, building tradesmen, millrights and machinists.
If the drill point angle and/or the cutting lip relief angle needs to be different than standardized geometry to more efficiently drill a softer material such as wood or plastic which is generally drilled with a 90.degree. point or a hard metal such as manganese bronze which is generally drilled with a 135.degree. point, then the geometry must be changed by regrinding before the new drill is used.
Good quality high-speed steel twist drills are expensive, for example, the average current list price for 1/8 inch size is about $0.60, for 5/16 inch size about $1.75 and for 1/2 inch size about $4.00. Yet, only a very small percentage of the twist drills purchased are ever resharpened because it is very difficult for even a master machinist to resharpen the cutting lips by hand and produce the most efficient geometry. Generally, drills resharpened by hand remove material inefficiently, quickly become overheated, lose their sharpness and are scraped.
For these reasons thousand of small manufacturers scrap a number of twist drills per day and at an estimated average cost of $2.00 each. Such loss can amount to a hundred and more dollars per week per manufacturer.
The size of possibly not less than 85 percent of all twist drills manufactured and used are within the range of 1/16 inch to 1/2 inch diameter and within this range there are 29 fractional inch sizes, 26 letter sizes, 56 numeral sizes, and 140 millimeter sizes, and one of the main objects of this invention is to provide a drill sharpener whereby all of these different sizes of drills, about 250 in all, can be handled by one relatively inexpensive drill holding chuck, instead of having to use 250 different sizes of collets for handling each of the 250 different sizes of drills as is the general practice with most prior art drill sharpeners.